Аннотация:A long-standing debate among scientists, environmental managers, and makers of federal public policy has centered on the causes and cures of rapid erosion on the Navajo Indian Reservation (Arizona, New Mexico, and Utah). Federal and tribal policies that address erosion problems have not accounted for the importance of climatic change because supporting data were unconvincing and because of a national preoccupation with the soil conservation-overgrazing relationship. Political and economic concerns in Southern California have influenced hydrologic and geomorphologic research in the Colorado River Basin and the reservation because of interest in irrigation and hydroelectrical power development associated with Hoover Dam. Preliminary analysis of recently developed hydrologic and climatic records shows that adjustments in southwestern regional climate directly affected fluvial processes through variation in surface moisture conditions as measured by the Palmer Drought Severity Index. Variation in the index over a test period of 1930-1960 explained 38% to 66% of the variation of water and sediment yields from the Little Colorado and San Juan rivers. Stocking levels as recorded in reservation management documents explained 1 % to 5% of the variation in water and sediment yields in this arid and semiarid area. Hydroclimatic change is therefore much more significant than land management in explaining changes in fluvial processes.
